In order to achieve the end of the HIV epidemic, concerted efforts will be needed to address the HIV care continuum, including improving retention in care and viral suppression among persons living with HIV (PLWH). Currently, in the U.S., it is estimated that less than 50% of PLWH are retained in care and even fewer are virally suppressed. Studies have shown that these PLWH have poorer clinical outcomes and are at risk of transmitting HIV to others, hence the need for innovative solutions to improve retention in care and subsequent viral suppression. Theory-based mHealth interventions have been shown to be promising in reaching these at- risk groups and improving HIV-related outcomes. PositiveLinks is a clinic-deployed mHealth platform that includes patient and provider smartphone apps, a web portal for clinic staff and providers to manage patient cohorts, an online implementation guide, and a learning management system to train and certify clinic staff. It has theory-based features including daily queries of adherence, mood, and stress, graphical feedback for self- monitoring, secure messaging with staff, appointment reminders, anonymized peer support, information resources, and document upload capability to support insurance re-enrollment. A 12-month prospective study in poorly retained adults with HIV found that PL increased RIC and VS, with app usage related to benefit as well as improved social support and stigma. PL is a promising existing mHealth tool for PLWH, but its efficacy has not been tested in a rigorous randomized trial, nor in urban populations. We propose to test the efficacy of PositiveLinks to improve retention in care and viral suppression among a cohort of PLWH in a high HIV prevalence city of Washington, DC. Participants will be identified from the DC Cohort, a longitudinal observational prospective cohort of PLWH receiving HIV care at 14 clinical sites in Washington, DC. First, we will conduct formative research to assess the feasibility, acceptability and usability of PositiveLinks among this urban cohort and conduct subsequent adaptations based on these findings. We will then conduct an efficacy study through a cluster randomized controlled trial at 14 DC Cohort sites among 560 PLWH. Clinics will be randomized to PL or usual care. Our primary outcomes will include viral suppression, retention in care and visit constancy at 12 months. Finally, we will conduct mixed methods implementation science research guided by the Consolidated Framework for Implementation Research and RE-AIM to identify site, patient, provider, and system factors that characterize best practices in program implementation. If successful, this research will lead to the development of a novel and efficacious approach to improving retention in care and viral suppression among PLWH which could lead to next-generation dissemination research that will contribute to HIV epidemic control. This project is responsive to NIH priorities, National HIV/AIDS Strategy, and Ending the HIV Epidemic goals as it is cross-cutting, seeks to reduce health inequities, and to improve health outcomes to achieve sustained viral suppression in a geographic hotspot for HIV.